Letter of Undertaking is commonly known as LUT. The Letter of Undertaking (LUT) is prescribed to be furnished in precribed form , whereby the exporter declares that he/she would fulfil all the requirements prescribed under GST while exporting without making IGST payment. Filing Letter of Undertaking is mandatory to export goods or service or both without payment of Integrated Taxes (IGST). If LUT has not been furnished, the export can only be made through payment of IGST or by furnishing an export bond.